Method for automatically determining document position in a scanner window

ABSTRACT

A method for determining the position of a document placed in the scanning widow of a flatbed scanner is disclosed. The method can correctly determine the precise position of a document from a pre-scanned image, including portions of a pressing cover (background color), illuminator (different color from the background) and the document. By color identification, a preliminary range having a rectangular area covering the document and the illuminator is first determined. Then, the colors of the four corners of the preliminary range are identified. Finally, the precise position of the document is determined by color identification, approaching from the rim of the preliminary range toward the the document.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention generally relates to an automatic method for a scanner,and more particularly relates to a method for determining the positionof a document placed in the scanning widow of a flatbed scanner.

2. Related Art

Automatic methods for a flatbed scanner to determine the position of adocument placed on the scanner window are already well known. However,the prior methods are limited to the application of flatbed scannersthat have a single background pattern of the scanner window. In otherwords, the prior method obtains a background image pattern of thescanner window by a pre-scanning process, then the background imagepattern (a certain image color) can be omitted later from automaticranged scanning so as to produce the document image only. When the priormethod is applied to a flatbed scanner with two kinds (two colors) ofbackground image pattern, incorrect determining of the document rangemay occur.

For example, beside a common black or white pressing cover for theflatbed, a conventional scanner may include an illuminator for lightinga transparency or a film for scanning. The illuminator has a colordifferent from that of the pressing cover. Therefore, with the priormethod the scanner mistakes the image of the illuminator as a part ofthe scanned document if only one background color (the color of thepressing cover) is considered. Or, a partial image of the scanneddocument is cropped if two background colors are considered.

SUMMARY OF THE INVENTION

The object of the invention is therefore to provide a method fordetermining the position of a document placed on a flatbed scanner inwhich the background image of the flatbed includes two color regions.

The method of the invention includes two steps for finding the scanneddocument. The first step is to locate a preliminary range of scanning.The preliminary range is determined from the rim toward the center ofthe scanner window. The preliminary range is a rectangular area coveringthe hardware (the illuminator) and the document located within thescanner window. The second step is to determine the portion of thedocument in the preliminary region by sampling certain points andcomparing the relative position of the preliminary range to the centerof the illuminator, then determining the precise position of thedocument by approaching the document in that portion through coloridentification.

Further scope of applicability of the invention will become apparentfrom the detailed description given hereinafter. However, it should beunderstood that the detailed description and specific examples, whileindicating preferred embodiments of the invention, are given by way ofillustration only, since various changes and modifications within thespirit and scope of the invention will become apparent to those skilledin the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will become more fully understood from the detaileddescription given hereinbelow. However, this description is for purposesof illustration only, and thus is not limitative of the invention,wherein:

FIG. 1 is a hardware constructional view of a flatbed scanner;

FIGS. 2-1 to 2-5 are examples of scanned images of different sizeddocuments placed in the scanner window;

FIGS. 3-1 to 3-7 are examples of scanned images with documents placed indifferent portions of the scanner window;

FIG. 4 is a flowchart showing the major steps of the invention;

FIGS. 5-1 to 5-5 are examples of preliminary ranges of scanning;

FIG. 6 is an example of locating a preliminary range of scanning;

FIG. 7 shows four reference points at the corners of a preliminary rangeof scanning;

FIGS. 8-1 to 8-28 are examples of relative positions between documentsand the illuminator;

FIGS. 9-1 and 9-2 are examples of relative positions of documents to thecenter of the illuminator;

FIGS. 10-1 to 10-6 are examples of finding out the positions ofdocuments in the preliminary regions.

DETAILED DESCRIPTION OF THE INVENTION

As shown in FIG. 1, a general flatbed scanner 10 includes a scannerwindow 10 that is usually transparent glass. A pressing cover 20 isremovably mounted on the scanner window 10. On the pressing cover 20, atthe surface facing the scanner window 10, there is an illuminator 21 forilluminating a transparency, film or the like, for the scanner to obtainan image. The illuminator 21 is usually located in the middle of thepressing cover 20, and has a certain position relative to the scannerwindow 10. The pressing cover 20 has a specific color, usually black orwhite, at the surface facing the scanner window 10. Meanwhile, the colorof the illuminator 21 is different from that of the pressing cover 20,according to the construction and material thereof.

The size and position of a scanned document D relative to the scannerwindow 10 and the illuminator 21 influences the result of the automaticdetermining of document position. Firstly, an example is shown in FIGS.2-1 to 2-3 in which three different sized documents D are placed underthe illuminator 21. The sizes of the documents D are larger than, equalto and smaller than the size of the illuminator 21 in the three figures.In FIG. 2-1, the document D is larger than the illuminator 21 and ispositioned to totally cover the range of the illuminator 21, so thatonly the background color of the pressing cover 20 is exposed on the rimof image of the document D. This is the simplest condition for which theaforesaid prior method can process automatic range-finding correctly.The same condition occurs in FIG. 2-2 that the document D is the samesize as the illuminator 21 and is positioned right on the range of theilluminator 21. When the size of the document D is smaller than that ofthe illuminator 21, the position of the document D partially overlapsthe illuminator 21 (as shown in FIG. 3-1), is totally free from theilluminator 21 (as shown in FIG. 3-7), or is fully enclosed in the rangeof the illuminator 21 (as shown in FIG. 2-3). In these cases, thescanned image includes the colors of the pressing cover 20, theilluminator 21 and the document D. The image with multiple backgroundcolors cannot be correctly processed by the prior method. Therefore, theinvention intends to solve this problem and provides a method fordetermining finding the correct position of document D out of thecomplex background.

Even when the document D is larger than or the same size as theilluminator 21, it is still possible, as shown in FIG. 2-4 and 2-5, bythe position of the document D, that the scanned image includes colorsof the pressing cover 20, the illuminator 21 and the document D, asdescribed above.

The method for determining the position of document D in the scannedimage with two background colors according to the invention is describedbelow.

As with a conventional flatbed scanner, the scanner of the inventionfirst pre-scans the scanner widow 10 with a document D placed thereon,and obtains a pre-scanned image that includes images of the pressingcover 20, the illuminator 21 and the document D. FIGS. 3-1 to 3-7 areexamples of pre-scanned images in which the documents D are placed indifferent portions of the scanner window.

After obtaining the pre-scanned image, the invention processes thefollowing steps to locate the position of the document D. The process isdescribed in reference to the flowchart of FIG. 4. First, in step A, apreliminary range 1 of scanning is located. The preliminary range 1 isdetermined from the rim toward the center of the scanner window 10. Thepreliminary range 1 is an area covering the illuminator 21 and thedocument D located within the scanner window 10. Because the backgroundcolor of the pressing cover 20 is a single one (black or white), theregions of the document D and the illuminator 21 can be determined bycolor identification, which will be described later. FIGS. 5-1 to 5-5are examples of preliminary ranges 1 for different locations of documentD relative to the illuminator 21.

Since most documents are rectangular in shape, in order to speed up therecognition process, the area of the preliminary ranges 1 is alsopreferably rectangular and a minimum one including images of theilluminator 21 and the document D. The process for obtaining thepreliminary ranges 1 of FIGS. 5-1 to 5-5 is illustrated with FIG. 6, forexample.

As shown in FIG. 6, to beginning from one side of the scanned image,searches along one axis (for example, the X-axis) of the X-Y coordinatesto verify the color of the pixels on each column. If the pixels in thewhole column with the same X-coordinate have the same color as thebackground color of the pressing cover 20, then the next column issearched until a column of pixels that includes a different color, forexample at column X1, is located. Then a rim X1 of the document D or theilluminator 21 is obtained. It further searches the following columnsuntil the column Xe, where the whole column pixels revert to the colorof the pressing cover 20. Then the column X2 (=Xe-1), which is thecolumn before Xe, is determined to be the other rim of the preliminaryrange 1.

Using the same process as above to search along the other axis (forexample, the Y-axis) of the X-Y coordinates and verify the color of thepixels on each row, the rim rows of the preliminary range 1 in Y-axis,marked Y1 and Y2, can also be obtained. Therefore, the coordinates offour corners of the preliminary range 1 are P1(X1,Y2), P2(X2,Y2),P3(X2,Y1) and P4(X1,Y1). In other words, the four points enclose aminimum area covering the document D and the illuminator 21 as thepreliminary range 1.

Steps B to E, as shown in FIG. 4, are used to determine the detailedposition of the document D. In step B, the relationship between thedocument and the pressing cover 20 is encoded (converted into numericalcodes). As shown in FIG. 7, the colors of the four corner points P1 toP4 of the preliminary range 1 are registered with numerical codes, sothat “1” represents the same color as the pressing cover 20, and “0”represents a color different from that. Therefore, a serial number, like(0,0,0,1), indicates the position of the document D relative to theilluminator 21. FIGS. 8-1 to 8-28 are examples of the identificationcodes in accordance with the positional relationship between thedocument D and the illuminator 21.

The step C is to determine the positional relationship between thecenter point 211 of the illuminator 21 and the center point 10 of thepreliminary range 1. Since the physical position of the illuminator 21is fixed, we can use the origin point “0” of the coordinates of thescanner window as the origin of the center point 10 of the preliminaryrange 1 and the center point 211 of the illuminator 21 so that theposition of the preliminary range 1 relative to the illustrator 21 canbe identified. For example, the coordinates of the center 211 of theilluminator 21 can be expressed as (Xm, Ym); the center point 10 of thepreliminary range 1 can be calculated as [(X2-X1)/2, (Y2−Y1)/2] from thecorner coordinates thereof. The two points, as shown in FIGS. 9-1 and9-2, can be used to determine the direction of the document D in thepreliminary range 1.

Step D is to determine the direction of the document D in thepreliminary range 1 for approaching the detailed position of thedocument D in the next step. The determination is based on the aforesaididentification codes of the document D and the illuminator 21 in thepreliminary range 1, and the aforesaid coordinates of the centers 211,10 of the illuminator 21 and the preliminary range 1. For example, inFIG. 9-1, the preliminary range 1 has an identification code of(0,1,0,0). The center point 10 of the preliminary range 1 is located atthe right of the center point 211 of the illuminator 21. According tothe positions of the four corners P1 to P4, the points P2 and P3 arelocated at the right side of the preliminary range 1. By referring tothe values (1 and 0) of the points P2 and P3, we can judge that thedocument D is located at the lower right corner of the preliminary range1 because P2=1 indicates that there is the background color of thepressing cover 20, and P3=0 indicates the existence of the document D.By the same process, the document D of FIG. 9-2 can be found at theupper left corner of the preliminary range 1.

FIGS. 8-1 to 8-4 show special positional relationships between thepreliminary range 1 and the illuminator 21 in which the centers thereofoverlap, and the identification codes are (0, 0, 0, 0) and (1, 1, 1, 1).In these conditions, the dimensions of the preliminary range 1 and theilluminator 21 have to be compared. In FIGS. 8-1 and 8-2, theidentification codes are (0, 0, 0, 0), and the dimensions of thepreliminary range 1 are the same as or larger than that of theilluminator 21. Therefore, the document D fully overlaps the preliminaryrange 1 or is smaller and is located in the center of the preliminaryrange 1. In FIGS. 8-3 and 8-4, the identification codes are (1, 1, 1, 1)and the width of the preliminary range 1 is larger or smaller than thatof the illuminator 21. Therefore, the document D lies horizontally orvertically across the preliminary range 1.

Step E is to determine the precise position of the document D bysearching the boundary of the document D from the rim of the preliminaryrange 1 in the direction toward the document D. For example, in FIG.10-1, the identification code based on the four corners P1 to P4 is (0,0, 0, 0). The length and width of the document D are smaller than thatof the illuminator 21. Therefore, the document D is located in themiddle of the preliminary range 1. The precise position of the documentD can be determined by searching downward from the top edge, upward fromthe bottom edge, leftward from the right edge and rightward from theleft edge of the preliminary range 1. When the pixels of the image ineach row or column include two or more colors, the edge of document D inthat direction is found. After this process, the image portions of theilluminator 21 in the preliminary range 1 are cropped, and the portionof the document D is obtained.

In FIG. 10-2, the identification code based on the four corners P1 to P4is (1, 0, 1, 0). The center point 10 of the preliminary range 1 islocated in the lower-left side of the center point 211 of theilluminator 21. Therefore, the document D is located in the lower-leftcorner of the preliminary range 1. The precise position of the documentD can be determined by searching downward from the top edge and leftwardfrom the right edge of the preliminary range 1 to locate the top andright edges of the document D. When the pixels of the image in the rowor column include two or more colors, the edge of document D in thatdirection is found. After the top and right edges of the document D areobtained, the two edges and the left and bottom edges of the preliminaryrange 1 determine the position of the document D.

In FIG. 10-3, the identification code based on the four corners P1 to P4is (1, 0, 0, 1). The center point 10 of the preliminary range 1 islocated on the left side of the center point 211 of the illuminator 21.Therefore, the document D is located on the left side of the preliminaryrange 1. The precise position of the document D can be determined bysearching downward from the top edge, upward from the bottom edge andleftward from the right edge of the preliminary range 1 to locate thetop, bottom and right edges of the document D. When the pixels of theimage in the row or column include two or more colors, the edge ofdocument D in that direction is found. After the top, bottom and rightedges of the document D are obtained, the three edges and the left edgeof the preliminary range 1 determine the position of the document D.

In FIG. 10-4, the identification code based on the four corners P1 to P4is (0, 1, 0, 0). The center point 10 of the preliminary range 1 islocated on the right side of the center point 211 of the illuminator 21.Therefore, the document D is located on the lower-right corner of thepreliminary range 1. The precise position of the document D can bedetermined by searching downward from the top edge and rightward fromthe left edge of the preliminary range 1 to locate the top and leftedges of the document D. After the top and left edges of the document Dare obtained, the two edges and the right and bottom edges of thepreliminary range 1 determine the position of the document D.

In FIG. 10-5, the identification code based on the four corners P1 to P4is (1, 0, 0, 1). The center point 10 of the preliminary range 1 islocated on the right side of the center point 211 of the illuminator 21.Therefore, the document D is located on the right side of thepreliminary range 1. The precise position of the document D can bedetermined by searching rightward from the left edge of the preliminaryrange 1 to find out the left edge of the document D. After the left edgeof the document D is obtained, the left edge and the right, top andbottom edges of the preliminary range 1 determine the position of thedocument D.

In FIG. 10-6, the identification code based on the four corners P1 to P4is (1, 1, 1, 1). The width of the preliminary range 1 is larger than thewidth of the illuminator 21. Therefore, the document D lies horizontallyacross the preliminary range 1. The precise position of the document Dcan be determined by searching downward from the top edge and upwardfrom the bottom edge of the preliminary range 1 to locate the top andbottom edges of the document D. After the top and bottom edges of thedocument D are obtained, the two edges and the left and right edges ofthe preliminary range 1 determine the position of the document D.

As described above, the invention can correctly determine the preciseposition of a document from a pre-scanned image, including portions ofthe pressing cover, illuminator and the document.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

1.-6. (canceled)
 7. An apparatus, comprising: means for obtaining apre-scanned image, wherein the pre-scanned image includes a documentimage portion and a background image portion; means for determining apreliminary range of the pre-scanned image; means for distinguishing atleast a portion of said document image portion from said backgroundimage portion; and means for determining a position of the documentimage portion within the range of the pre-scanned image.
 8. Theapparatus of claim 7, wherein said means for determining saidpreliminary range further comprises means for locating one side of saidpre-scanned image, and means for searching along the one side toidentify at least one corner of the pre-scanned image.
 9. The apparatusof claim 7, wherein said means for distinguishing comprises means foridentifying color differences between said document image portion andsaid background image portion.
 10. The apparatus of claim 7, whereinmeans for distinguishing comprises means for identifying one or morecorners of the document image portion within the pre-scanned image. 11.The apparatus of claim 10, wherein means for identifying one or morecorners comprises means for identifying color differences between saiddocument image portion and said background image portion at the one ormore corners.
 12. The apparatus of claim 10, wherein means foridentifying one or more corners further comprises means for identifyinga center point of said document image portion.
 13. The apparatus ofclaim 7, wherein the document image portion and a background imageportion comprise different colors.
 14. The apparatus of claim 7, andfurther comprising means for distinguishing at least a portion of saiddocument image portion and/or said background image portion from anilluminated portion of the pre-scanned image.
 15. The apparatus of claim7, and further comprising means for determining the positionalrelationship between said document image portion and said backgroundimage portion within the range of the pre-scanned image.
 16. Anapparatus, comprising: circuitry to obtain a pre-scanned image of atleast a portion of a scanning object including a document portion and abackground portion; circuitry to determine a preliminary range of thepre-scanned image; circuitry to distinguish at least a portion of thepre-scanned image comprising said portion of the document from at leasta portion of the image comprising said portion of the background; andcircuitry to determine a position of the document portion within thepreliminary range of the pre-scanned image.
 17. The apparatus of claim16, and further comprising an illuminator adapted to illuminate thescanning object.
 18. The apparatus of claim 16, wherein said circuitryto determine a preliminary range further comprises circuitry to locateone side of said pre-scanned image, and searchalong the one side toidentify at least one corner of the pre-scanned image.
 19. The apparatusof claim 16, further comprising circuitry to identify at least one colordifference between said document portion and said background portion.20. The apparatus of claim 16, further comprising circuitry to identifya center point of said document portion.
 21. The apparatus of claim 16,wherein the document portion and a background portion comprise differentcolors.
 22. The apparatus of claim 16, further comprising circuitry todetermine a positional relationship between said document portion andsaid background portion within the preliminary range of the pre-scannedimage.
 23. An article comprising a computer readable storage mediumhaving stored thereon instructions that, when executed, result in:obtaining a pre-scanned image, wherein the pre-scanned image includes adocument image portion and a background image portion; determining apreliminary range of the pre-scanned image; distinguishing at least aportion of said document image portion from said background imageportion; and determining a position of the document image portion withinthe range of the pre-scanned image.
 24. The article of claim 23, whereinthe instructions, when executed, further result in determining saidpreliminary range by locating one side of said pre-scanned image, andsearching along the one side to identify at least one corner of thepre-scanned image.
 25. The article of claim 23, wherein theinstructions, when executed, further result in distinguishing byidentifying color differences between said document image portion andsaid background image portion.
 26. The article of claim 23, wherein theinstructions, when executed, further result in distinguishing byidentifying one or more corners of the document image portion within thepre-scanned image.
 27. The article of claim 26, wherein theinstructions, when executed, further result in identifying colordifferences between said document image portion and said backgroundimage portion at the one or more corners.
 28. The article of claim 26,wherein the instructions, when executed, further result in identifyingone or more corners by identifying a center point of said document imageportion.
 29. The apparatus of claim 23, wherein the document imageportion and a background image portion comprise different colors. 30.The article of claim 23, wherein the instructions, when executed,further result in determining the positional relationship between saiddocument image portion and said background image portion within therange of the pre-scanned image.